The present invention relates to insulated electrical wires, in particular for windings, which can be used in complete safety when totally immersed in water or in oil and which withstand water and hydrolysis.
Applications of such wires include submerged pumps, motors and pumps of domestic appliances such as washing machines, dishwashers and tumble dryers, automotive equipment, oil-filled transformers and wires in cables exposed to wet and/or oily environments.
Insulated electrical wires have a coating on their electrical conductor to provide electrical insulation of the electrical conductor and to enable the wire to withstand the environment. The coating is specific to the conditions of use of the wire.
Thus the coating of electrical wires which are totally immersed in water in use is formed of a relatively thick PVC layer extruded directly onto the electrical conductor. Because of the possibility of the PVC decomposing at higher temperatures, and the resulting pollution problems, PVC-coated wires have a relatively low thermal rating, less than 120xc2x0 C.
Electrical wires for windings which are used in a wet environment but which are not immersed unless this happens accidentally are often coated with one or more layers of enamel to obtain a wire of small cross-section. However, in the equipment concerned, such wires are associated with circuits which protect against short-circuits in the event of accidental contact with water.
The conductor of an electrical wire which is totally immersed in oil when in use is generally coated with at least one layer of enamel and there is at least one layer of paper on top of the enamel, the combination enabling the enameled wire to withstand hydrolysis.
An object of the present invention is to provide an insulated electrical wire which can be used in water or in oil, which uses a uniform type of coating used in comparable prior art wires which are totally immersed in such media in use, and which avoids the need for the protection circuits associated with the other prior art wires referred to above.
Another object of the invention is to provide an insulated electrical wire of the above kind whose final cross-section is small compared to that of comparable prior art wires which are totally immersed in use.
A further object of the present invention is to provide an insulated wire of the above kind with a high thermal rating.
According to the present invention the insulated wire capable of withstanding immersion in water and in oil comprises an electrical conductor and a coating on the conductor and said coating comprises an inner layer formed of at least one layer of enamel on said conductor and an outer layer of polyphenylene oxide on top of said inner layer.
The polyphenylene oxide outer layer is advantageously of polyphenylene oxide modified by a polystyrene.
Said outer layer of polyphenylene oxide, whether modified or not, is advantageously from 50 xcexcm to 250 xcexcm thick.
Said inner layer preferably includes two enamel layers.
Said outer layer of polyphenylene oxide, whether modified or not, is advantageously extruded onto said inner layer.
The features and advantages of the present invention emerge from the following description of an embodiment of the invention which is given by way of preferred but non-limiting example and with reference to the accompanying drawing.